package com.xisoft.common.enums;

import cn.hutool.core.date.format.FastDateFormat;

import java.net.InetAddress;
import java.net.UnknownHostException;


/**
 * 与snowflake算法区别,返回字符串id,占用更多字节,但直观从id中看出生成时间 改写了生成时间的format方法
 *
 * @version 1.0<br>
 * @qualiFild pers.bc.utils.pub.IdGenerator.java<br>
 * @author：licheng<br>
 * @date Created on 2020年4月3日<br>
 */
public enum IdGenerator
{

    INSTANCE;
    private long workerId; // 用ip地址最后几个字节标示
    private long datacenterId = 0L; // 可配置在properties中,启动时加载,此处默认先写成0
    private long sequence = 0L;
    private long workerIdBits = 8L; // 节点ID长度
    private long datacenterIdBits = 2L; // 数据中心ID长度,可根据时间情况设定位数
    private long sequenceBits = 12L; // 序列号12位
    private long workerIdShift = sequenceBits; // 机器节点左移12位
    private long datacenterIdShift = sequenceBits + workerIdBits; // 数据中心节点左移14位
    private long sequenceMask = -1L ^ (-1L << sequenceBits); // 4095
    private long lastTimestamp = -1L;
    private static final FastDateFormat FAST_DATE_FORMAT = FastDateFormat.getInstance("yyyyMMddHHmmssSSS");

    IdGenerator( )
    {
        workerId = 0x000000FF & getLastIP();
    }

    public synchronized String nextId( )
    {
        long timestamp = timeGen(); // 获取当前毫秒数
        // 如果服务器时间有问题(时钟后退) 报错。
        if (timestamp < lastTimestamp)
        {
            throw new RuntimeException(String.format(
                    "Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }
        // 如果上次生成时间和当前时间相同,在同一毫秒内
        if (lastTimestamp == timestamp)
        {
            // sequence自增，因为sequence只有12bit，所以和sequenceMask相与一下，去掉高位
            sequence = (sequence + 1) & sequenceMask;
            // 判断是否溢出,也就是每毫秒内超过4095，当为4096时，与sequenceMask相与，sequence就等于0
            if (sequence == 0)
            {
                timestamp = tilNextMillis(lastTimestamp); // 自旋等待到下一毫秒
            }
        }
        else
        {
            sequence = 0L; // 如果和上次生成时间不同,重置sequence，就是下一毫秒开始，sequence计数重新从0开始累加
        }
        lastTimestamp = timestamp;
        long suffix = (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
        // String datePrefix = DateFormatUtils.format(timestamp, "yyyyMMddHHmmssSSS");
        String datePrefix = FAST_DATE_FORMAT.format(timestamp);

        return datePrefix + suffix;
    }

    protected long tilNextMillis(long lastTimestamp)
    {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp)
        { timestamp = timeGen(); }

        return timestamp;
    }

    protected long timeGen( )
    {
        return System.currentTimeMillis();
    }

    private byte getLastIP( )
    {
        byte lastip = 0;
        try
        {
            InetAddress ip = InetAddress.getLocalHost();
            byte[] ipByte = ip.getAddress();
            lastip = ipByte[ipByte.length - 1];
        }
        catch (UnknownHostException e)
        {
            e.printStackTrace();
        }
        return lastip;
    }

}
